The present invention relates generally to cell searching in a mobile communication network and, more particularly, to methods and apparatus for identifying sources of signals during cell searching.
In a conventional mobile communication network, the coverage of the network area is divided into a plurality of cells. A base station with a centrally-located antenna provides service to user terminals within the cell. Each cell is identified by a unique cell ID, which is broadcast to the user terminals over a broadcast channel. The cell ID enables the user terminals to differentiate between different cells when implementing cell search algorithms for mobility management purposes.
A distributed antenna system (DAS) has been proposed for the Long Term Evolution (LTE) standard being developed by the 3rd Generation Partnership Project (3GPP). In a distributed antenna system, the base station connects to multiple antennas that provide coverage to user terminals within a cell. The area covered by each antenna, referred to herein as a subcell, is generally much smaller than that of a centrally-located antenna in a conventional mobile communication system. The distributed antenna system architecture has two main advantages. First, it is possible to achieve a high spatial re-use factor due to the small coverage area of each antenna. Second, the single base station has control over all of the radio resources used at each antenna and can therefore coordinate the transmission and reception of signals to minimize interference and increase system capacity.
Cell planning errors may result in two adjacent cells have the same cell ID, which is not desirable. For example, two different cells having the same cell ID may cause confusion in user terminals in systems that use distributed antenna systems. In this case, the user terminal may erroneously assume that a signal received from an antenna in an adjacent cell is from an antenna in a current serving cell. Mistakes of this nature could result in mobility management errors.
Accordingly, there is a need for a way to determine whether a detected signal originates in a known cell or a new cell having the same cell identifier as the known when cell planning errors occur.